FetchXML.cs

private static List<Entity> GetAccounts()
{
  string fetchXml = @"<fetch version='1.0' output-format='xml-platform' mapping='logical' distinct='true'>
                              <entity name='account'>
                                <attribute name='accountnumber' />
                                <attribute name='accountid' />
                                <attribute name='modifiedon' />
                                <order attribute='modifiedon' descending='true' />
                                <order attribute='name' descending='false' />
                              </entity>
                            </fetch>";
     return orgService.RetrieveAll(new FetchExpression(fetchXml));
}
        
public static List<Entity> RetrieveAll(this IOrganizationService service, FetchExpression query)
{
            var conversionRequest = new FetchXmlToQueryExpressionRequest
            {
                FetchXml = query.Query
            };

            var conversionResponse =
                (FetchXmlToQueryExpressionResponse)service.Execute(conversionRequest);

            return RetrieveAll(service, conversionResponse.Query);
}
        
 public static List<Entity> RetrieveAll(this IOrganizationService service, QueryExpression query)
 {
            var result = new List<Entity>();

            var entities = service.RetrieveMultiple(query);
            result.AddRange(entities.Entities);

            var page = 2;
            while (entities.MoreRecords)
            {
                query.PageInfo = new PagingInfo
                {
                    PagingCookie = entities.PagingCookie,
                    PageNumber = page
                };

                entities = service.RetrieveMultiple(query);
                result.AddRange(entities.Entities);
                page++;
            }

            return result;
}